The invention is directed to a method for clearing down a connection existing between a cordless terminal equipment and a switching equipment via a first base station and for simultaneously setting up a connection between this cordless terminal equipment and the switching equipment via a second base station, i.e. the handover of an existing connection from a first to a second base station. What is to be understood by this handover is what is referred to as a "connection handover" defined by the ETSI in the DECT Standard ETS 300 175-1 through ETS 300 175-11, particularly in ETS 300 175-4:1992, Chapter 9.2.7.3.
Such methods are implemented in communications systems having at least one switching equipment for setting up and clearing down connections between communication terminal equipment, whereby user information in the form of user signals can be respectively transmitted between the switching equipment and the communication terminal equipment within a connection, and the switching equipment can receive and output user signals transmitted in wire-bound fashion. A respective plurality of base stations connected to the switching equipment is provided in such communication systems in order to convert user signals transmittable in wire-bound fashion into wirelessly transmittable user signals, in order to output these user signals onto one of a plurality of selectable channels and in order to convert wirelessly transmittable user signals into user signals transmittable in wire-bound fashion. The base stations, called "Radio Fixed Part" (RFP) according to DECT, thus enable the realization of connections between communications terminal equipment designed as cordless terminal equipment (KES) that wirelessly transmit and receive signals, also called a mobile part, and the switching equipment.
The afore-mentioned DECT Standard provides that a cordless terminal equipment (mobile part) connected to the switching equipment via a first base station sends a "Connection Hand Over Request" to a second base station for initiating a connection setup between this mobile part and the switching equipment via this second base station. According to the DECT Standard, the mobile part must make B-channel data available, i.e. must send user signals to the second base station as soon as it has received a signal "Bearer Confirm" from this base station. At this point in time, B-channel data from the switching equipment are also available via this base station. Immediately after receipt of "Bearer Confirm", the mobile part must switch the reception to the second base station because it is defined in the DECT Standard that the previous connection can be cleared down at the system side after the error-free transmission of "Bearer Confirm", namely without signalization-wise release at the air interface between the base station and the mobile part (ETS 300 175-4:1992, Chapter 9.2.7.3). In the standardized connection handover, the previous connection is cleared down by the mobile part as per definition.
Whereas it is set down in the DECT Standard that responses to signalizations between mobile parts and base stations are to be assured within approximately five milliseconds by radio via the air interface, the corresponding response times between base stations and switching nodes are usually ten to a hundred times longer. Consequently, there is no exact information on hand in the switching node about the point in time at which a base station selected for a new connection sends the message "Bearer Confirm" to the corresponding mobile part, or respectively this mobile part receives said message. The selection of the point in time at which, given "connection handover", the user data reception should be switched from the previous base station to the new base station in the switching equipment is consequently problematical.
When the reception to user data in the switching equipment is immediately switched to the new base station after the switching equipment initiates the parallel transmission of the user data to both participating base stations, user data will not yet be made available by the mobile part via the new base station. When, by contrast, the switching equipment switches the user data reception over to the new base station only after receiving an acknowledgment of the new base station regarding the error-free transmission of the message "Bearer Confirm", then, as a reaction to "Bearer Confirm", the mobile part can, due to the longer signaling running time of the wire-bound transmission, have ended the transmission of user information via the original base station before the arrival of the acknowledgment message in the switching equipment and, thus, before a certain time span before the switching of the reception at the switching side.
In both described instances, a gap occurs within the user data transmission. When the user data are a matter of voice signals, then the seamless handover from one base station to the next described in the DECT Standard is not assured. In data transmission, certain data sequences drop out in the call handover, so that corresponding communication equipment can be used for data transmission only in conjunction with an involved error monitoring system.